Electronic unit and feed system

ABSTRACT

An electronic unit includes: a power receiving section configured to receive electric power fed from a feed unit by using a magnetic field; and a control section configured to perform, when a receiving current supplied from the power receiving section is less than a predetermined threshold current at a time of a light load, current increasing control to increase the receiving current to the threshold current or more.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication JP2013-80431 filed Apr. 8, 2013, and JP2013-188057 filedSep. 11, 2013, the entire contents of each of which are incorporatedherein by reference.

BACKGROUND

The present disclosure relates to a feed system that performsnon-contact electric power supply (feeding, or power transmission) to aunit to be fed such as an electronic unit. The present disclosure alsorelates to an electronic unit applied to such a feed system.

In recent years, attention has been given to a feed system (such as anon-contact feed system and a wireless charging system) that performsnon-contact electric power supply to a CE device (Consumer ElectronicsDevice) such as a mobile phone and a portable music player. This makesit possible to start charging merely by placing an electronic unit (asecondary-side unit) on a charging tray (a primary-side unit), insteadof starting charging by inserting (connecting) a connector of apower-supply such as an AC adapter into the unit. In other words,terminal connection between the electronic unit and the charging traybecomes unnecessary.

Methods of thus performing non-contact power supply are broadlyclassified into two types of methods. A first method is anelectromagnetic induction method that has been already widely known. Inthis method, a degree of coupling between a power transmission side (aprimary side) and a power receiving side (a secondary side) isconsiderably high and therefore, high-efficiency feeding is possible. Asecond method is a method called a magnetic resonance method. Thismethod has such a characteristic that a magnetic flux shared by thepower transmission side and the power receiving side may be small due topositive utilization of a resonance phenomenon.

Here, such non-contact feed systems are disclosed in WO 00/27531, aswell as Japanese Unexamined Patent Application Publication Nos.2001-102974, 2008-206233, 2002-34169, 2005-110399, and No. 2010-63245,for example.

SUMMARY

In the non-contact feed systems as described above, in general, a loadin an electronic unit to be fed fluctuates according to the situation offeeding and charging. Therefore, it is expected to propose a methodcapable of performing appropriate control in response to a fluctuationof a load, when performing feeding by using a magnetic field.

It is desirable to provide an electronic unit and a feed system that arecapable of performing appropriate control when performing feeding usinga magnetic field.

According to an embodiment of the present disclosure, there is providedan electronic unit including: a power receiving section configured toreceive electric power fed from a feed unit by using a magnetic field;and a control section configured to perform, when a receiving currentsupplied from the power receiving section is less than a predeterminedthreshold current at a time of a light load, current increasing controlto increase the receiving current to the threshold current or more.

According to an embodiment of the present disclosure, there is provideda feed system provided with one or a plurality of electronic units and afeed unit configured to feed the electronic units by using a magneticfield. Each of the electronic units includes: a power receiving sectionconfigured to receive electric power fed from the feed unit; and acontrol section configured to perform, when a receiving current suppliedfrom the power receiving section is less than a predetermined thresholdcurrent at a time of a light load, current increasing control toincrease the receiving current to the threshold current or more.

In the electronic unit and the feed system according to theabove-described respective embodiments of the present disclosure, whenthe receiving current at the time of the light load is less than thepredetermined threshold current, the current increasing control isperformed to increase the receiving current to the threshold current ormore. This allows a receiving voltage to be readily controlled in anappropriate manner, even at the time of the light load.

According to the electronic unit and the feed system of theabove-described respective embodiments of the present disclosure, whenthe receiving current at the time of the light load is less than thepredetermined threshold current, the current increasing control isperformed to increase the receiving current to the threshold current ormore. Therefore, even at the time of the light load, the receivingvoltage is allowed to be controlled readily in an appropriate manner.Hence, appropriate control is allowed to be performed when feeding usinga magnetic field is performed. It is to be noted that effects are notlimited to those described here, and may include every effect describedin the present disclosure.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments and, together with the specification, serve to describe theprinciples of the technology.

FIG. 1 is a perspective view illustrating an appearance configurationexample of a feed system according to an embodiment of the presentdisclosure.

FIG. 2 is a diagram illustrating a detailed configuration example of thefeed system illustrated in FIG. 1.

FIG. 3 is a circuit diagram illustrating a detailed configurationexample of an AC signal generating circuit illustrated in FIG. 2.

FIG. 4 is a timing waveform diagram illustrating an example of a controlsignal for the AC signal generating circuit.

FIG. 5A is a circuit diagram schematically illustrating an operationexample of the AC signal generating circuit illustrated in FIG. 3.

FIG. 5B is a circuit diagram schematically illustrating anotheroperation example of the AC signal generating circuit illustrated inFIG. 3.

FIG. 6 is a circuit diagram illustrating a detailed configurationexample of a dummy load circuit illustrated in FIG. 2.

FIG. 7 is a circuit diagram schematically illustrating a state exampleof the dummy load circuit illustrated in FIG. 6.

FIG. 8 is a characteristic diagram illustrating an example of arelationship between a phase difference, and a receiving voltage as wellas a load resistance, in the AC signal generating circuit.

FIG. 9 is a characteristic diagram used to describe an influence of aharmonic.

FIG. 10 is a flowchart illustrating an example of feeding and chargingoperation according to the embodiment.

FIG. 11 is a flowchart illustrating an example of the feeding andcharging operation following FIG. 10.

FIG. 12 is a diagram illustrating an example of an operating state inpreliminary feeding.

FIG. 13 is a diagram illustrating an example of a relationship between areceiving current and a connection state of a dummy load.

FIG. 14 is a circuit diagram schematically illustrating another stateexample of the dummy load circuit illustrated in FIG. 6.

FIG. 15A is a circuit diagram schematically illustrating still anotherstate example of the dummy load circuit illustrated in FIG. 6.

FIG. 15B is a circuit diagram schematically illustrating still anotherstate example of the dummy load circuit illustrated in FIG. 6.

FIG. 16 is a flowchart illustrating an example of processing ofdisconnecting a dummy load according to Modification 1.

FIG. 17 is a diagram illustrating an example of a relationship between areceiving current and a connection state of a dummy load according toModification 2.

FIG. 18 is a diagram illustrating a configuration example of a feedsystem according to Modification 3.

FIG. 19 is a block diagram illustrating a configuration example of acurrent increasing control section illustrated in FIG. 18.

FIG. 20 is a circuit diagram illustrating a configuration example of thecurrent increasing control section illustrated in FIG. 19.

FIG. 21A is a circuit diagram illustrating a detailed configurationexample of the current increasing control section illustrated in FIG.20.

FIG. 21B is a circuit diagram illustrating another detailedconfiguration example of the current increasing control sectionillustrated in FIG. 20.

FIG. 22A is a block diagram illustrating a state example of the currentincreasing control section illustrated in FIG. 19.

FIG. 22B is a block diagram illustrating another state example of thecurrent increasing control section illustrated in FIG. 19.

FIG. 23 is a characteristic diagram illustrating an example of ameasurement result according to Modification 3.

FIG. 24 is a characteristic diagram illustrating another example of themeasurement result according to Modification 3.

FIG. 25 is a diagram illustrating an example of a relationship between areference voltage and each parameter according to Modification 3.

FIG. 26 is a circuit diagram illustrating a configuration example of acurrent increasing control section according to Modification 4.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below indetail with reference to the drawings. It is to be noted that thedescription will be provided in the following order.

-   1. Embodiment (an example of a case in which a receiving current is    increased utilizing a dummy load)-   2. Modifications

Modification 1 (an example of a case in which disconnection of a dummyload is determined according to a magnitude of a receiving current)

Modification 2 (an example of a case in which selection from a pluralityof types of dummy loads is performed according to a magnitude of areceiving current, and the selected type of dummy load is utilized)

Modifications 3 and 4 (examples of a case in which a receiving currentis increased using a comparator and an integrator)

-   3. Other modifications    [Embodiment]    [Overall Configuration of Feed System 4]

FIG. 1 illustrates an appearance configuration example of a feed system(a feed system 4) according to an embodiment of the present disclosure,and FIG. 2 illustrates a detailed configuration example of the feedsystem 4, by using a block diagram and a circuit diagram. The feedsystem 4 is a system (a non-contact type feed system) that performselectric power transmission (power supply, feeding, or powertransmission) in a non-contact manner by using a magnetic field (byutilizing magnetic resonance, electromagnetic induction, or the like;likewise hereinafter). The feed system 4 includes a feed unit 1 (aprimary-side unit) and a plurality of electronic units (here, oneelectronic unit 2; a secondary-side unit) serving as a unit to be fed.

In the feed system 4, electric power transmission from the feed unit 1to the electronic unit 2 may be performed by placing the electronic unit2 on (or, in proximity to) a feeding surface (a power transmissionsurface) S1 in the feed unit 1, as illustrated in FIG. 1, for example.Here, as an example, the feed unit 1 is shaped like a mat (a tray) inwhich the area of the feeding surface S1 is larger than the electronicunit 2 to be fed.

(Feed Unit 1)

The feed unit 1 is a unit (a charging tray) that performs the feeding tothe electronic unit 2 by using a magnetic field as described above. Thefeed unit 1 may include a power transmission section 10, an AC(alternating-current) signal generating circuit (an AC signal generatingsection, or a high-frequency power generating circuit) 11, acommunication section 12, and a control section 13, as illustrated inFIG. 2, for example.

The power transmission section 10 may include, for example, a powertransmission coil (a primary-side coil) L1, a capacitor C1 (a capacitorfor resonance), and the like. The power transmission coil L1 and thecapacitor C1 are electrically connected in series to each other.Specifically, one end of the power transmission coil L1 is connected toone end of the capacitor C1, and the other end of the power transmissioncoil L1 is grounded. The other end of the capacitor C1 is connected toan output terminal of the AC signal generating circuit 11. The powertransmission section 10 performs feeding by utilizing an AC magneticfield to the electronic unit 2 (specifically, a power receiving section20 that will be described later), by utilizing the power transmissioncoil L1 and the capacitor C1 (see an arrow P1 in FIG. 2). Specifically,the power transmission section 10 has a function of emitting a magneticfield (a magnetic flux) from the feeding surface S1 towards theelectronic unit 2.

Further, in the power transmission section 10, an LC resonance circuitis configured using the power transmission coil L1 and the capacitor C1.The LC resonance circuit formed in the power transmission section 10 andan LC resonance circuit formed in the power receiving section 20 thatwill be described later are magnetically coupled to each other (mutualinduction).

The AC signal generating circuit 111 may be, for example, a circuit thatgenerates a predetermined AC signal Sac (high-frequency electric power)used to perform feeding, by using electric power (a direct-current (DC)signal Sdc) supplied from an external power source 9 (a host powersource) of the feed unit 1. The AC signal Sac is supplied towards thepower transmission section 10. It is to be noted that examples of theexternal power source 9 may include an ordinary AC adapter, and a USB(Universal Serial Bus) 2.0 power source (power supply ability: 500 mA,and power supply voltage: about 5 V) provided in a PC (PersonalComputer), etc.

As will be described later, for example, the AC signal generatingcircuit 11 as described above may be configured using a switchingamplifier (a so-called class E amplifier, a differential amplifier, orthe like) including one or a plurality of switching elements SW1 thatare MOS (Metal Oxide Semiconductor) transistors and/or the like.Further, a control signal CTL for feeding is supplied from the controlsection 13 to the switching element SW1. It is to be noted that adetailed configuration of the AC signal generating circuit 11 will bedescribed later.

The communication section 12 performs predetermined mutual communicationoperation with a communication section 26 in the electronic unit 2 (seean arrow C1 in FIG. 2). The communication section 26 will be describedlater.

The control section 13 performs various kinds of control operation inthe entire feed unit 1 (the entire feed system 4). Specifically, otherthan controlling the power transmission operation performed by the powertransmission section 10 and the communication operation performed by thecommunication section 12, the control section 13 may have, for example,a function of controlling optimization of feeding power andauthenticating a unit to be fed. The control section 13 may further havea function of detecting the unit to be fed located in the proximity ofthe feed unit 1, and a function of detecting a mixture such asdissimilar metal, etc. Here, when performing the above-described controlof the feeding operation, the control section 13 controls operation ofthe AC signal generating circuit 11, by using the control signal CTLdescribed above. The control section 13 as described above may beconfigured using, for example, a microcomputer, a pulse generator, orthe like. It is to be noted that the operation of controlling the ACsignal generating circuit 11 by the control section 13 will be describedlater in detail.

(Electronic Unit 2)

The electronic unit 2 may be, for example, any of stationary electronicunits represented by television receivers, portable electronic unitscontaining a rechargeable battery represented by mobile phones anddigital cameras, and the like. As illustrated in, for example, FIG. 2,the electronic unit 2 may include the power receiving section 20, arectification circuit 21, a current detection section 22, a dummy loadcircuit 23, a charging section 24, a battery 25, the communicationsection 26, a control section 27, and a memory section 28. It is to benoted that the dummy load circuit 23 corresponds to a specific but notlimitative example of “current increasing section” in the presentdisclosure.

The power receiving section 20 includes a power receiving coil (asecondary-side coil) L2 as well as capacitors C2 s and C2 p (capacitorsfor resonance). The power receiving coil L2 and the capacitor C2 s areelectrically connected in series to each other, whereas the powerreceiving coil L2 and the capacitor C2 p are electrically connected inparallel to each other. Specifically, one end of the capacitor C2 s isconnected to one input terminal of the rectification circuit 21 and oneend of the capacitor C2 p. The other end of the capacitor C2 s isconnected to one end of the power receiving coil L2. The other end ofthe power receiving coil L2 is connected to the other input terminal ofthe rectification circuit 21 and the other end of the capacitor C2 p.The power receiving section 20 has a function of receiving electricpower (feeding power) transmitted from the power transmission section 10in the feed unit 1, by utilizing the power receiving coil L2, thecapacitors C2 s and C2 p, and the like.

Further, in the power receiving section 20, an LC resonance circuit isconfigured using the power receiving coil L2 as well as the capacitorsC2 s and C2 p. As described above, the LC resonance circuit formed inthe power receiving section 20 and the above-described LC resonancecircuit formed in the power transmission section 10 are magneticallycoupled to each other. As a result, LC resonance operation is performedbased on a resonance frequency that is substantially the same as that ofthe high-frequency electric power (the AC signal Sac) generated by theAC signal generating circuit 11.

The rectification circuit 21 rectifies a receiving voltage (an ACvoltage) supplied from the power receiving section 20, and generates aDC voltage. In other words, the rectification circuit 21 rectifies an ACreceiving current (an AC receiving current Iac) and an AC receivingvoltage (an AC receiving voltage Vac) supplied from the power receivingsection 20, and generates a DC receiving current (a DC receiving currentIdc) and a DC receiving voltage (a DC receiving voltage Vdc). Therectification circuit 21 may be, for example, a circuit having a bridgeconfiguration using a plurality of rectifiers (diodes). It is to benoted that the rectification circuit 21 may be, for example, asynchronous rectification circuit using a transistor.

The current detection section 22 detects the receiving current suppliedfrom the power receiving section 20. In this example, in particular, thecurrent detection section 22 is provided on a subsequent stage side ofthe rectification circuit 21 on a power supply line Lp, to detect thereceiving current (the DC receiving current Idc) after the rectificationby the rectification circuit 21. The DC receiving current Idc thusdetected is outputted to the control section 27. It is to be noted that,for example, the current detection section 22 as described above may beconfigured using a resistor, a current transformer, etc.

The dummy load circuit 23 is disposed between the rectification circuit21 and the charging section 24 on the power supply line Lp, and includesone or a plurality of dummy loads (such as dummy resistors). When apredetermined condition described later is satisfied, the dummy loadcircuit 23 performs operation (current increasing operation) ofincreasing the receiving current (the DC receiving current Idc, in thisexample), according to control by (a control signal CTL2 from) thecontrol section 27. It is to be noted that a detailed configuration ofthe dummy load circuit 23 and details of the current increasingoperation will be described later.

Based on DC power outputted from the rectification circuit 21, thecharging section 24 performs charging operation of charging the battery25 serving as a main load.

The battery 25 stores electric power according to the charging operationperformed by the charging section 24, and may be configured using, forexample, a rechargeable battery (a secondary battery) such as a lithiumion battery.

The communication section 26 performs the above-described predeterminedmutual communication operation with the communication section 12 in thefeed unit 1 (see the arrow C1 in FIG. 2).

The control section 27 performs various kinds of control operation inthe entire electronic unit 2 (the entire feed system 4). Specifically,other than controlling the power receiving operation by the powerreceiving section 20 and the communication operation performed by thecommunication section 26, the control section 27 may have, for example,a function of controlling optimization of receiving power andcontrolling the charging operation of the charging section 24.

Here, in the present embodiment, the control section 27 performs currentincreasing control as will be described below, in a case where thereceiving current (the DC receiving current Idc) detected by the currentdetection section 22 is less than a predetermined threshold current Ith(Idc<Ith), at the time of a light load that will be described later.Specifically, in such a case, the control section 27 performs thecurrent increasing control so that the DC receiving current Idcincreases to the threshold current Ith or more (Idc≧Ith). To be morespecific, for example, the control section 27 may perform such currentincreasing control, by using one or more of the dummy loads in the dummyload circuit 23 described above. The control section 27 as describedabove may be configured using, for example, a microcomputer. It is to benoted that the current increasing control operation by the controlsection 27 will be described later in detail.

The memory section 28 is provided to store therein various kinds ofinformation used in the control section 27. Specifically, the memorysection 28 may store therein, for example, information about theabove-described threshold current Ith.

[Detailed Configuration Example of AC Signal Generating Circuit 11]

Next, a detailed configuration example of the above-described AC signalgenerating circuit 11 will be described with reference to FIGS. 3, 4,5A, and 5B. FIG. 3 illustrates a circuit configuration example of the ACsignal generating circuit 11, together with the external power source 9,the power transmission section 10, and the control section 13.

In this example, the AC signal generating circuit 11 has a bridgecircuit configuration using four switching elements SW1 a, SW1 b, SW1 c,and SW1 d as the above-described switching element SW1. Further, theswitching elements SW1 a, SW1 b, SW1 c, and SW1 d each are configured ofa MOS transistor in this example. In the AC signal generating circuit11, the switching elements SW1 a, SW1 b, SW1 c, and SW1 d haverespective gates to which control signals CTL1 a, CTL1 b, CTL1 c, andCTL1 d, respectively, are inputted individually as the above-describedcontrol signal CTL1. A connection line from the external power source 9is connected to a source of each of the switching elements SW1 a and SW1c. A drain of the switching element SW1 a is connected to a drain of theswitching element SW1 b, and a drain of the switching element SW1 c isconnected to a drain of the switching element SW1 d. The switchingelements SW1 b and SW1 d have respective sources connected to a ground(grounded). Furthermore, the switching elements SW1 a and SW1 b haverespective drains connected to one end of the capacitor C1 in the powertransmission section 10, and the switching elements SW1 c and SW1 d haverespective drains connected to one end of the power transmission coil L1in the power transmission section 10.

Here, the above-described control signal CTL1 (CTL1 a, CTL1 b, CTL1 c,and CTL1 d) may be a pulse signal indicating a predetermined frequency f(CTL1 (f)=f1) and a duty ratio Duty (CTL1 (Duty)=10%, 50%, etc.), asillustrated in FIG. 4, for example. Further, as illustrated in FIG. 4,pulse width modulation (PWM) is performed by controlling the duty ratioDuty in the control signal CTL1.

In the AC signal generating circuit 11, with such a configuration, theswitching elements SW1 a, SW1 b, SW1 c, and SW1 d each perform ON/OFFoperation (switching operation based on the frequency f and the dutyratio Duty) according to the control signals CTL1 a, CTL1 b, CTL1 c, andCTL1 d. In other words, the ON/OFF operation of the switching elementSW1 is controlled using the control signal CTL1 supplied from thecontrol section 13. As a result, for example, the AC signal Sac may begenerated based on the DC signal Sdc inputted from the external powersource 9 side, and the generated AC signal Sac may be supplied to thepower transmission section 10.

Further, in the AC signal generating circuit 11, it is possible toswitch the circuit configuration between a full-bridge circuit and ahalf-bridge circuit in the following manner, according to the controlsignals CTL1 a, CTL1 b, CTL1 c, and CTL1 d. This makes it possible tochange a voltage in feeding, based on control of the switchingoperation, without changing a hardware configuration.

Specifically, for example, as illustrated in FIG. 5A, the configurationof the full-bridge circuit may be used when the four switching elementsSW1 a, SW1 b, SW1 c, and SW1 d each perform the ON/OFF operation.

Further, as illustrated in FIG. 5B, for example, there may be a case inwhich, while the two switching elements SW1 a and SW1 b each perform theON/OFF operation, the switching element SW1 c is typically in an OFFstate and the switching element SW1 d is typically in an ON state. Thisis equivalent to the configuration of the half-bridge circuit includingthe two switching elements SW1 a and SW1 b. Therefore, in this case, avoltage (a feeding voltage) generated by the AC signal generatingcircuit 11 in feeding is about half of that in the case of thefull-bridge circuit illustrated in FIG. 5A. It is to be noted that FIGS.5A and 5B as well as subsequent similar drawings schematicallyillustrate each of the switching elements in the form of a switch, foreasy understanding of an operating state thereof.

[Detailed Configuration Example of Dummy Load Circuit 23]

Next, a detailed configuration example of the above-described dummy loadcircuit 23 will be described with reference to FIGS. 6 and 7. FIG. 6illustrates a circuit configuration example of the dummy load circuit23, together with the control section 27.

In this example, the dummy load circuit 23 includes two dummy loads Raand Rb each being a resistor (a dummy resistor), and two switchingelements SW2 a and SW2 b each being configured of a MOS transistor. Thedummy load Ra and the switching element SW2 a are connected in series toeach other between the power supply line Lp and a ground line. The dummyload Rb and the switching element SW2 b are connected in series to eachother between the power supply line Lp and the ground line.Specifically, one end of the dummy load Ra is connected to the powersupply line Lp, the other end of the dummy load Ra is connected to adrain of the switching element SW2 a, and a source of the switchingelement SW2 a is connected to the ground line. Similarly, one end of thedummy load Rb is connected to the power supply line Lp, the other end ofthe dummy load Rb is connected to a drain of the switching element SW2b, and a source of the switching element SW2 b is connected to theground line. Further, a pair of the dummy load Ra and the switchingelement SW2 a are arranged in parallel with a pair of the dummy load Rband the switching element SW2 b. Furthermore, the control signals CTL2 aand CTL2 b are individually inputted as the above-described controlsignal CTL2, to gates of the switching elements SW2 a and SW2 b,respectively.

With such a configuration, in the dummy load circuit 23, the twoswitching elements SW2 a and SW2 b are individually set to be in an ONstate or in an OFF state, according to the control signals CTL2 a andCTL2 b, respectively, supplied from the control section 27. As a result,in the dummy load circuit 23, the two dummy loads Ra and Rb areindividually connected or not connected to a point in a supply path(between the power supply line Lp and the ground line) of the DCreceiving current Idc.

In is to be noted that, for example, as illustrated in FIG. 7, theswitching elements SW2 a and SW2 b both may be set in the OFF state, ata time other than the above-described time of the light load (other thanthe case of satisfying (Idc<Ith), which will be described later). Inother words, the dummy loads Ra and Rb are both set not to be connectedto the points in the supply path of the DC receiving current Idc.

[Functions and Effects of Feed System 4]

(1. Summary of Entire Operation)

In the feed system 4, the predetermined high-frequency electric power(the AC signal Sac) used to perform the electric power transmission issupplied by the AC signal generating circuit 11 in the feed unit 1, tothe power transmission coil L1 and the capacitor C1 in the powertransmission section 110. This supply is based on the electric powersupplied from the external power source 9. As a result, a magnetic field(a magnetic flux) occurs in the power transmission coil L1 in the powertransmission section 10. At this moment, when the electronic unit 2serving as the unit to be fed is placed on (or, in proximity to) the topsurface (the feeding surface S1) of the feed unit 1, the powertransmission coil L1 in the feed unit 1 and the power receiving coil L2in the electronic unit 2 are in proximity to each other in the vicinityof the feeding surface S1.

In this way, when the power receiving coil L2 is placed in proximity tothe power transmission coil L1 generating the magnetic field, anelectromotive force (an induced electromotive force) is generated in thepower receiving coil L2 by being induced by the magnetic flux generatedby the power transmission coil L1. In other words, due toelectromagnetic induction or magnetic resonance, the magnetic field isgenerated by forming interlinkage with each of the power transmissioncoil L1 and the power receiving coil L2. As a result, electric power istransmitted from the power transmission coil L1 side (a primary side,the feed unit 1 side, or the power transmission section 10 side) to thepower receiving coil L2 side (a secondary side, the electronic unit 2side, or the power receiving section 210 side) (see the arrow P1 in FIG.2). At this moment, the power transmission coil L1 on the feed unit 1side and the power receiving coil L2 on the electronic unit 2 side aremagnetically coupled to each other by electromagnetic induction or thelike, and the LC resonance operation is performed.

Then, in the electronic unit 2, the AC power received by the powerreceiving coil L2 is supplied to the charging section 24 through therectification circuit 21, and the charging operation is performed asfollows. First, an AC voltage (AC current) is converted into apredetermined DC voltage (DC current) by the rectification circuit 21.Then, the charging of the battery 25 based on the DC voltage isperformed by the charging section 24. In this way, the chargingoperation based on the electric power received by the power receivingsection 210 is performed in the electronic unit 2.

In other words, in the present embodiment, at the time of charging theelectronic unit 2, terminal connection to an AC adapter or the like, forexample, is unnecessary, and it is possible to start the charging easilyby merely placing the electronic unit 2 on (or in proximity to) thefeeding surface S1 of the feed unit 1 (non-contact feeding isperformed). This reduces burden on a user.

Moreover, in such operation, the mutual communication operation isperformed between the communication section 12 in the feed unit 1 andthe communication section 26 in the electronic unit 2 (see the arrow C1in FIG. 2). Therefore, for example, mutual authentication between theunits, and feeding efficiency control are performed.

(2. Receiving Current at Light Load)

Meanwhile, in the feed unit 1 of the present embodiment, feeding-powercontrol using the above-described PWM control is performed in the ACsignal generating circuit 11 (see FIG. 4). However, when suchfeeding-power control using the PWM control is performed, the receivingpower may not be appropriately controlled in the electronic unit 2 atthe time of the light load.

It is to be noted that, in the PWM control, in general, changing a phasedifference of input to a switching element is equivalent to changing aduty ratio. For example, when the phase difference of input is 90degrees, this may be equivalent to the duty ratio of 25%.

Here, FIG. 8 illustrates an example of a relationship between a phasedifference of input to the switching elements SW1 a to SW1 d in the ACsignal generating circuit 11, and the DC receiving voltage Vdc as wellas a load resistance in the electronic unit 2. As illustrated in FIG. 8,when a certain amount of current (the DC receiving current Idc) flows inthe electronic unit 2 (when a value of the load resistance is small tosome extent), the DC receiving voltage Vdc becomes small as the phasedifference becomes small. In other words, in such a case, there is amonotone decreasing relationship between the phase difference and the DCreceiving voltage Vdc. However, when the current flowing in theelectronic unit 2 decreases (when the value of the load resistanceincreases), this monotone decreasing relationship disappears.

This is because, when the DC receiving current Idc becomes small (if theload becomes light), this makes it easy to see a frequency component ofmultiple resonance in the electronic unit 2, which increases aninfluence of a harmonic. Specifically, for example, as illustrated inFIG. 9, ratios between a fundamental content and a harmonic contentgreatly differ depending on the duty ratio. While the duty ratiomonotonously increases to 50% for the fundamental content, the dutyratio for the harmonic content does not monotonously increase.Therefore, for example, the ratio of a specific harmonic content in afundamental wave may become high in some cases. In this way, in a casein which the multiple resonance occurs in the electronic unit 2, whenthe load becomes light (when the value of the DC receiving current Idcbecomes small), the influence of a harmonic may increase. As a result,adjustment of the receiving voltage (the DC receiving voltage Vdc andthe like) may become difficult in the feeding of the electric powerbased on the PWM control. In other words, the light load in theelectronic unit 2 may bring the DC receiving voltage Vdc into anuncontrollable state, or cause the DC receiving voltage Vdc to become anovervoltage.

Here, in the feed system 4 of the present embodiment, the load in theelectronic unit 2 to be fed fluctuates depending on the situation of thefeeding and/or the charging, as will be described later. Therefore, itis desirable to perform appropriate control in response to fluctuationof the load, when the feeding is performed using a magnetic field. It isto be noted that in a case of control other than the feeding-powercontrol using the PWM control, when the load in the electronic unit 2 istoo light, it may be likewise difficult to adjust the receiving voltage(the DC receiving voltage Vdc and the like) due to a narrow voltagecontrol range in the feed unit 1.

(3. Operation of Increasing Receiving Current)

Therefore, in the present embodiment, the above-described disadvantageis addressed in the following manner, in the electronic unit 2 servingas the secondary-side unit.

When the DC receiving current Idc detected by the current detectionsection 22 is less than the predetermined threshold current Ith(Idc<Ith) at the time of the light load, the control section 27 in theelectronic unit 2 performs the following current increasing control.Specifically, in such a case, the control section 27 performs thecurrent increasing control, to increase the DC receiving current Idc tothe threshold current Ith or more (Idc≧Ith). To be more specific, thecontrol section 27 performs such current increasing control, by usingone or more of the dummy loads in the dummy load circuit 23. A series ofsteps in feeding and charging operation including such currentincreasing control will be described below in detail.

Here, for example, the following two periods each may be assumed to be“at the time of the light load” described above. First, there is aperiod before the battery 25 serving as the main load is connected (aperiod of preliminary feeding at the time of activation, which will bedescribed later; a first period). Secondly, there is a period of thecharging operation for the battery 25 based on main feeding that will bedescribed later (for example, a period of almost full charge; a secondperiod). This second period follows the connection of the battery 25.

Therefore, in the present embodiment, as will be described below indetail, it is determined whether a load is a light load (whether the DCreceiving current Idc is less than the threshold current Ith) in both ofthe period of the preliminary feeding and the period of the chargingoperation. Further, as will be described later, it is periodicallydetermined whether the load is a light load, in the period of thecharging operation. When it is determined that the load is a light load,the above-described current increasing control is performed.

FIG. 10 and FIG. 11 each illustrate the feeding and charging operationof the present embodiment, by using a flowchart. In the feeding andcharging operation, at first, the preliminary feeding begins (step S101in FIG. 10). In the preliminary feeding, electric power lower than thatin the main feeding is fed from the feed unit 1 to the electronic unit2. The electronic unit 2 is activated using the receiving power obtainedby this preliminary feeding (step S102).

Next, the receiving power in the main feeding is determined in theelectronic unit 2 (the control section 27), by communication between thefeed unit 1 and the electronic unit 2 (step S103). It is to be notedthat, in this preliminary feeding, necessary feeding power is lower thanthat in the main feeding and therefore, the AC signal generating circuit11 in the feed unit 1 is set to the half-bridge circuit.

Here, in such preliminary feeding, for example, as illustrated in FIG.12, the charging section 24 is control to be in a non-operating state bythe control section 27, which sets the main load (the battery 25 in thisexample) to a state of being not connected to the power supply line Lp.

Next, in the electronic unit 2, the current detection section 22 detectsthe DC receiving current Idc in the preliminary feeding (step S104),before notifying a request for start of the main feeding based on thereceiving power determined in step S103 to the feed unit 1 side (stepS106 to be described later). The control section 27 then determineswhether the detected DC receiving current Idc is less than thepredetermined threshold current Ith (Idc<Ith) (step S105). It is to benoted that the DC receiving current Idc in the preliminary feeding maybe estimated beforehand as a consumption current in an integratedcircuit (IC), unlike the charging operation that will be describedlater. Therefore, in steps S104 and S105 described above, a value thusestimated and set beforehand may be read from the memory section 28, forexample, and used in place of the current detected by the currentdetection section 22.

The threshold current Ith is set to be a current value that avoids apossibility of the receiving voltage being brought into anuncontrollable state, or a possibility of the receiving voltage becomingan overvoltage, due to the light load, as described with reference toFIG. 8, for example. For example, it is conceivable to set the thresholdcurrent Ith to about 100 mA. Further, the value of the threshold currentIth is not limited to a fixed value, and may be, for example, a variablevalue as described below (a configuration in which a value is variable).Specifically, for example, as indicated by an arrow P2 in FIG. 13, thevalue of the threshold current Ith may be set to vary according to themagnitude of the receiving voltage (the DC receiving voltage Vdc)supplied from the power receiving section 20 and rectified (for example,to control a load resistance value in the electronic unit 2 to be equalto or less than a constant value).

Here, when it is determined that the detected DC receiving current Idcis equal to or more than the threshold current Ith (Idc≧Ith) (step S105:N), it may be said that there is no possibility of the receiving voltagebeing brought into an uncontrollable state, or no possibility of thereceiving voltage becoming an overvoltage, due to the light load, asdescribed with reference to FIG. 8, for example. Therefore, in thiscase, the electronic unit 2 notifies the feed unit 1 of the request forstart of the main feeding by utilizing communication (step S106),without performing the current increasing control to be described below.In other words, in this case, as illustrated in FIG. 7 described above,in the dummy load circuit 23, the dummy loads Ra and Rb both remain setin the state of being not connected to the points in the supply path ofthe DC receiving current Idc (see a current range A2 illustrated in FIG.13).

On the other hand, when it is determined that the detected DC receivingcurrent Idc is less than the threshold current Ith (Idc<Ith) (step S105:Y), the current increasing control is performed in the electronic unit 2as follows.

First, for example, as illustrated in FIG. 14, the control section 27connects one or both of the dummy load Ra and the Rb (in this example,only the dummy load Ra) in the dummy load circuit 23, to the point inthe supply path of the DC receiving current Idc (step S107, see acurrent range A1 illustrated in FIG. 13). Specifically, the controlsection 27 controls the switching element SW2 a to be in the ON state,and the switching element SW2 b to be in the OFF state. As a result, asillustrated in FIG. 14, a current Ia flows to the dummy load Ra throughthe supply path (the power supply line Lp) of the DC receiving currentIdc, and thus the DC receiving current Idc is increased. In this way,control of increasing the DC receiving current Idc (the currentincreasing control) is performed.

After such current increasing control is performed, the control section27 determines whether the DC receiving current Idc detected again isless than the threshold current Ith (Idc<Ith) (step S108). Here, when itis determined that the DC receiving current Idc detected again is equalto or more than the threshold current Ith (Idc≧Ith) (step S105: N),namely, when the DC receiving current Idc is increased to the thresholdcurrent Ith or more by the current increasing control, the flow proceedsto step S106 described above. In other words, the electronic unit 2notifies the feed unit 1 of the request for start of the main feeding,by utilizing communication. This is because, in this case as well, itmay be said that there is no possibility of the receiving voltage beingbrought into an uncontrollable state, or no possibility of the receivingvoltage becoming an overvoltage, due to the light load.

On the other hand, when it is determined that the DC receiving currentIdc detected again is also less than the threshold current Ith (Idc<Ith)(step S108: Y), namely, when the DC receiving current Idc detected againis still less than the threshold current Ith even after the currentincreasing control is performed, the current increasing control isperformed again in the following manner. In other words, the controlsection 27 additionally connects the dummy load to the point in thesupply path of the DC receiving current Idc in the dummy load circuit23, or switches the dummy load to the dummy load having a larger load(for example, a larger resistance value) (step S109). It is to be notedthat after such second-time current increasing control, the flow returnsto step S108.

Here, the case of additionally connecting the dummy load may be,specifically, as illustrated in FIG. 15A, for example. In this example,the control section 27 connects the dummy load Rb, in addition to thedummy load Ra, to the point in the supply path of the DC receivingcurrent Idc. To be more specific, the control section 27 controls theswitching elements SW2 a and SW2 b to be both in the ON state. As aresult, as illustrated in FIG. 15A, the current Ia and a current Ib flowto the dummy loads Ra and Rb, respectively, through the supply path ofthe DC receiving current Idc, thereby further increasing the DCreceiving current Idc. In this way, the control of further increasingthe DC receiving current Idc is performed.

On the other hand, the case of switching the dummy load to a larger loadmay be, specifically, as illustrated in FIG. 15B, for example. In thisexample, when the load of the dummy load Rb is larger than that of thedummy load Ra, the control section 27 connects the dummy load Rb,instead of the dummy load Ra, to the point in the supply path of the DCreceiving current Idc. To be more specific, the control section 27controls the switching element SW2 a to be in the OFF state and theswitching element SW2 b to be in the ON state. As a result, asillustrated in FIG. 15B, the current Ib flows the dummy load Rb havingthe larger load through the supply path of the DC receiving current Idc,thereby further increasing the DC receiving current Idc. In this way,the control of further increasing the DC receiving current Idc isperformed.

Here, after the request for start of the main feeding is notified to thefeed unit 1 side (step S106) as described above, the main feeding inwhich the electric power is higher than that in the preliminary feedingis then started to feed the electric power from the feed unit 1 to theelectronic unit 2 (step S110). In other words, in this main feeding, theAC signal generating circuit 11 in the feed unit 1 is switched from thehalf-bridge circuit to the full-bridge circuit.

When the main feeding is thus started, the control section 27 switchesthe charging section 24 to an operating state, thereby setting thebattery 25 serving as the main load to be connected to the power supplyline Lp in the electronic unit 2 (step S111). Further, in this stepS111, when setting the battery 25 to be in the state of being connected,the control section 27 disconnects both of the dummy loads Ra and Rbfrom the points in the supply path of the DC receiving current Idc.Specifically, as illustrated in FIG. 7 described above, the controlsection 27 controls the switching elements SW2 a and SW2 b to be both inthe OFF state. As a result, the currents Ia and Ib do not flow to thedummy loads Ra and Rb, respectively, and the control of increasing theDC receiving current Idc is stopped.

Next, in the electronic unit 2, the charging section 24 performs thecharging operation in which the battery 25 is charged based on thereceiving power (the main feeding) (step S112 in FIG. 11). The controlsection 27 then determines whether the battery 25 is fully charged bythe charging operation (step S113). Here, when it is determined that thebattery 25 is fully charged (step S113: Y), the feeding and chargingoperation illustrated in FIG. 10 and FIG. 11 ends.

On the other hand, when it is determined that the battery 25 is notfully charged (step S113: N), the control section 27 then determineswhether the DC receiving current Idc detected again at the chargingoperation is less than the threshold current Ith (Idc<Ith) (step S114).Here, when it is determined that the DC receiving current Idc detectedagain is equal to or more than the threshold current Ith (Idc≧Ith) (stepS114: N), the above-described current increasing control is notperformed, and the flow returns to step S112.

On the other hand, when it is determined that the DC receiving currentIdc detected again is less than the threshold current Ith (Idc<Ith)(step S114: Y), the control section 27 performs the current increasingcontrol by the above-described technique (the technique of connectingthe dummy load) (step S115). After performing such current increasingcontrol, the control section 27 then determines again whether the DCreceiving current Idc is less than the threshold current Ith (Idc<Ith)(step S116).

Here, when it is determined that the DC receiving current Idc is equalto or more than the threshold current Ith (Idc≧Ith) (step S116: N),namely, when the DC receiving current Idc is increased to the thresholdcurrent Ith or more by the current increasing control, the flow returnsto step S112 described above.

On the other hand, when it is determined that the DC receiving currentIdc is less than the threshold current Ith (Idc<Ith) (step S116: Y),namely, when the DC receiving current Idc is still less than thethreshold current Ith even after the current increasing control isperformed, the control section 27 performs the current increasingcontrol again by the above-described technique (the techniqueillustrated in either FIG. 15A or FIG. 15B, for example). Specifically,the control section 27 additionally connects the dummy load to the pointin the supply path of the DC receiving current Idc in the dummy loadcircuit 23, or switches the dummy load to the dummy load having a largerload (step S117). It is to be noted that after such second-time currentincreasing control, the flow returns to step S116.

As described above, in the present embodiment, when the DC receivingcurrent Idc at the time of the light load is less than the predeterminedthreshold current Ith, the current increasing control is performed toincrease the DC receiving current Idc to the threshold current Ith ormore. This makes it possible to control the receiving voltage (such asthe DC receiving voltage Vdc) in the electronic unit 2 readily in anappropriate manner, even at the time of the light load. Specifically, itis possible to avoid the possibility of the receiving voltage beingbrought into an uncontrollable state, or the possibility of thereceiving voltage becoming an overvoltage, due to the light load, asdescribed with reference to FIG. 8, for example. Therefore, it ispossible to perform appropriate control when the feeding is performed byusing a magnetic field.

[Modifications]

Next, modifications (Modifications 1 to 4) of the above-describedembodiment will be described. It is to be noted that the same elementsas those in the embodiment will be provided with the same referencenumerals as those thereof, and the description thereof will be omittedappropriately.

[Modification 1]

FIG. 16 is a flowchart illustrating an example of processing ofdisconnecting the dummy load according to Modification 1. Unlike theabove-described embodiment, in the present modification, the controlsection 27 disconnects the dummy load from the point in the supply pathof the DC receiving current Idc when the DC receiving current Idc isequal to or more than the threshold current Ith (Idc≧Ith) after thebattery 25 is set to be in a connection state. In other words, thecontrol section 27 disconnects the dummy load, upon confirming themagnitude of the DC receiving current Idc again after the battery 25 isset to be in the connection state.

It is to be noted that the processing illustrated in FIG. 16 may be, forexample, processing replacing the processing in steps S111 and S112 inthe above-described embodiment. Otherwise, a series of steps in feedingand charging operation in the present modification is basically similarto that in the above-described embodiment.

In the processing of disconnecting the dummy load of the presentmodification, at first, in a manner similar to that of the embodiment,when the battery 25 serving as the main load is connected in theelectronic unit 2 (step S201 in FIG. 16), the operation of charging thebattery 25 is performed (step S202). However, in the presentmodification, the dummy load is not yet disconnected at this stage,unlike the above-described embodiment.

Subsequently, in the electronic unit 2, it is determined again whetherthe DC receiving current Idc detected at this stage is less than thethreshold current Ith (Idc<Ith) (step S203). Here, when it is determinedthat the detected DC receiving current Idc is less than the thresholdcurrent Ith (Idc<Ith) (step S203: Y), the load is still a light load.Therefore, the dummy load is not yet disconnected at this stage, and theflow returns to step S202.

On the other hand, when it is determined that the detected DC receivingcurrent Idc is equal to or more than the threshold current Ith (Idc≧Ith)(step S203: N), the control section 27 then performs control todisconnect the dummy load (step S204). This ends the processing ofdisconnecting the dummy load illustrated in FIG. 16.

In this way, in the present modification, the dummy load is disconnectedupon the confirmation of the magnitude of the DC receiving current Idcagain, after the battery 25 is set to be in the connection state.Therefore, in addition to the effects in the above-described embodiment,it is possible to obtain the following effect, for example. First, whenthe battery 25 serving as the main load is set to be in the connectionstate, the main load is a heavy load and therefore, like theabove-described embodiment, the dummy load may be desirably disconnectedat this moment. However, depending on the situation, the load may be ina light-load state even after the main load is connected. Therefore, thetiming of disconnecting the dummy load may be controlled appropriatelyaccording to the situation, by adopting the above-described technique ofthe present modification. Hence, it is possible to perform the controlmore appropriately when the feeding is performed by using a magneticfield.

[Modification 2]

FIG. 17 illustrates an example of a relationship between the receivingcurrent (the DC receiving current Idc) and the connection state of thedummy load according to Modification 2. In the present modification, thedummy load circuit 23 includes a plurality of types (three types, inthis example) of dummy loads different in magnitude of load (theresistance value or the like) from one another. When it is determinedthat the DC receiving current Idc is less than the threshold currentIth, the control section 27 performs the current increasing control byconnecting the dummy load of the type that is selected from theplurality of types of dummy loads according to the magnitude of the DCreceiving current Idc, to the point in the supply path of the DCreceiving current Idc.

Specifically, the control section 27 connects the dummy load having arelatively large load, as the DC receiving current Idc becomes small. Inother words, in the example illustrated in FIG. 17, the control section27 connects the dummy load by switching the type of the dummy load inthe order of a small load, a middle load, and a large load, as the valueof the DC receiving current Idc less than the threshold current Ithbecomes small (according to shifting in the order of a current rangeA11, a current range A12, and a current range A13).

In this way, in the present modification, the dummy load of the typeselected from the plurality of types of dummy loads different inmagnitude of load from one another is connected, according to themagnitude of the detected DC receiving current Idc. Therefore, it ispossible to perform more-precise current increasing control.

It is to be noted that, in the example illustrated in FIG. 17, the threetypes of dummy loads different in magnitude of load from one another areused, but the types are not limited to three. Two types, or four or moretypes of dummy loads different in magnitude of load from one another maybe used.

[Modification 3]

(Configuration)

FIG. 18 illustrates a configuration example of a feed system (a feedsystem 4A) according to Modification 3, by using a block diagram and acircuit diagram. The feed system 4A of the present modification includesthe feed unit 1 and an electronic unit 2A. In other words, the feedsystem 4A corresponds to the feed system 4 including the electronic unit2A in place of the electronic unit 2, and is similar thereto in terms ofother configurations.

As illustrated in FIG. 18, the electronic unit 2A corresponds to theelectronic unit 2 including a current increasing control section 23A inplace of the dummy load circuit 23, and a control section 27A in placeof the control section 27. The electronic unit 2A is similar to theelectronic unit 2 in terms of other configurations. The control section27A corresponds to the control section 27 configured not to perform theabove-described current increasing control, and is similar thereto interms of other configurations. Further, the current increasing controlsection 23A performs current increasing control to be described below inplace of the control section 27, and corresponds to a specific but notlimitative example of “control section” in the present disclosure.

FIG. 19 illustrates a configuration example of the current increasingcontrol section 23A, by using a block diagram. FIG. 20 illustrates aconfiguration example of the current increasing control section 23Aillustrated in FIG. 19, by using a circuit diagram. Further, FIGS. 21Aand 21B each illustrate a detailed configuration example of the currentincreasing control section 23A illustrated in FIG. 20, by using acircuit diagram, together with a circuit configuration example of thecurrent detection section 22.

As will be described later, the current increasing control section 23Ais a circuit (an automatic load control section) that actively performsthe current increasing control, to increase the DC receiving current Idcto the threshold current Ith or more (Idc≧Ith). In other words, thecurrent increasing control is performed to prevent the DC receivingcurrent Idc from becoming less than the threshold current Ith (Idc<Ith).As illustrated in FIG. 19, the current increasing control section 23Aincludes a reference-voltage output section 231, a comparator 232, anintegrator 233, and a transistor 234.

Here, before description of these configurations in the currentincreasing control section 23A, a circuit configuration example of thecurrent detection section 22 in the present modification will bedescribed with reference to FIGS. 20, 21A, and 21B. In the presentmodification, the current detection section 22 detects the current (theDC receiving current Idc) as the voltage (the DC receiving voltage Vdc),and may include, for example, a resistor 22R and an amplifier 22A. Theresistor 22R is provided to be inserted in the supply path (the powersupply line Lp) of the DC receiving current Idc. Wiring connected to oneend side of the resistor 22R is connected to a positive-side (+) inputterminal of the amplifier 22A, and wiring connected to the other endside of the resistor 22R is connected to a negative-side (−) inputterminal of the amplifier 22A. Further, from an output terminal of theamplifier 22A, the detected DC receiving current Idc is outputted as theDC receiving voltage Vdc.

As illustrated in FIG. 20, for example, the reference-voltage outputsection 231 may be a circuit that outputs a reference voltage Vrefcorresponding to the threshold current Ith, and may include tworesistors 231R1 and 231R2. An input voltage Vin1 to be described lateris inputted to one end of the resistor 231R1, and the other end of theresistor 231R1 is connected to one end of the resistor 231R2 and anegative-side input terminal of the comparator 232 to be describedlater. The other end of the resistor 231R2 is grounded. With such aconfiguration, in the reference-voltage output section 231, the inputvoltage Vin1 is divided according to a resistance ratio between theresistors 231R1 and 231R2, and outputted as the reference voltage Vref.Specifically, when the resistors 231R1 and 231R2 are assumed to haverespective resistance values R11 and R12, the reference voltage Vref isexpressed by the following expression (1).Vref=Vin1×{R12/R11+R12)}  (1)

Here, there may be a case in which a predetermined fixed voltage Vcnstis used as the input voltage Vin1 (Vin1=Vcnst) as illustrated in FIG.21A, for example. There may also be a case in which the DC receivingvoltage Vdc that is a variable voltage is used as the input voltage Vin1(Vin1=Vdc) as illustrated in FIG. 21B, for example.

In the example of FIG. 21A, in the reference-voltage output section 231,the reference voltage Vref that is a constant voltage is generated bydividing the fixed voltage Vcnst according to the above-describedresistance ratio. On the other hand, in the example of FIG. 21B, in thereference-voltage output section 231, the reference voltage Vref that isa variable voltage is generated by dividing the DC receiving voltage Vdcaccording to the above-described resistance ratio. This variable voltagevaries in connection with a change in the DC receiving voltage Vdc.

As illustrated in FIG. 19, the comparator 232 is a circuit that comparesthe magnitude (electric potential) of the DC receiving voltage Vdccorresponding to the DC receiving current Idc, with that of thereference voltage Vref corresponding to the threshold current Ith, andthe comparator 232 then outputs an output signal (an output voltageVout) indicating a result of the comparison. In the comparator 232, asillustrated in FIGS. 19 to 21B, the DC receiving voltage Vdc is inputtedto a positive-side input terminal thereof, the reference voltage Vref isinputted to a negative-side input terminal thereof, and the outputvoltage Vout is outputted from an output terminal thereof.

The integrator 233 is a circuit (an active LPF (Low Pass Filter), or aPI (Proportional Integral) control circuit) that performs the currentincreasing control to be described later. The integrator 233 performsthe current increasing control by generating the control signal CTL3 ofthe transistor 234, based on the output voltage Vout supplied from thecomparator 232, and outputting the generated control signal CTL3.Specifically, the integrator 233 generates the control signal CTL3 bymultiplying the output voltage Vout sent from the comparator 232.

The integrator 233 may include, for example, four resistors 233R1,233R2, 233R3, and 233R4, a capacitor 233C, and an amplifier 233A, asillustrated in FIGS. 20, 21A, and 21B. An input voltage Vin3 is inputtedto one end of the resistor 233R1, and the other end of the resistor233R1 is connected to one end of the resistor 233R2 and a positive-sideinput terminal of the amplifier 233A. The other end of the resistor233R2 is grounded. Further, one end of the resistor 233R3 is connectedto an output terminal of the comparator 232, and the other end of theresistor 233R3 is connected to a negative-side input terminal of theamplifier 233A and one end of each of the capacitor 233C and theresistor 233R4. The other end of each of the capacitor 233C and theresistor 233R4 is connected to an output terminal of the amplifier 233Aand a gate of the transistor 234 to be described later.

The transistor 234 operates according to control by the control signalCTL3 supplied from the integrator 233, and is configured of a MOStransistor in this example. However, for example, the transistor 234 maybe a bipolar transistor, or the like. As illustrated in FIGS. 19 to 21B,the control signal CTL3 is inputted to the gate of the transistor 234,one of a source and a drain thereof is connected to the supply path (thepower supply line Lp) of the DC receiving current Idc, and the other isgrounded. As will be described later in detail, in the transistor 234,such a configuration makes it possible to flow a current between thepower supply line Lp and the ground according to the control of a gatevoltage by the control signal CTL3.

(Functions and Effects)

In the feed system 4A of the present modification, the followingoperation (the current increasing control) is performed in the currentincreasing control section 23A.

First, based on the output signal (the output voltage Vout) from thecomparator 232, the integrator 233 in the current increasing controlsection 23A determines whether the DC receiving voltage Vdc at the timeof the light load described above is less than the reference voltageVref (whether Vdc<Vref is satisfied). In other words, the integrator 233determines whether the DC receiving current Idc at the time of the lightload is less than the threshold current Ith (whether Idc<Ith issatisfied).

Here, when it is determined that Vdc≧Vref (Idc≧Ith) is satisfied, it maybe said that there is no possibility of the receiving voltage beingbrought into an uncontrollable state, or no possibility of the receivingvoltage becoming an overvoltage, due to the light load, as describedabove. Therefore, in this case, the current increasing control to bedescribed below is not performed in the current increasing controlsection 23A. In other words, in this case, the transistor 234 is set inan OFF state according to a control signal CT3 outputted from theintegrator 233, and a current does not flow to the transistor 234, asillustrated in FIG. 22A, for example.

On the other hand, when it is determined that Vdc<Vref (Idc<Ith) issatisfied, it may be said that there is a possibility of the receivingvoltage being brought into an uncontrollable state, or a possibility ofthe receiving voltage becoming an overvoltage, due to the light load, asdescribed above. Therefore, in this case, the current increasing controlto be described below is performed in the current increasing controlsection 23A. Specifically, in such a case, the integrator 233 sets thetransistor 234 in an ON state based on the control signal CT3, andconnects the transistor 234 to the supply path (the power supply lineLp) of the DC receiving current Idc, as illustrated in FIG. 22B, forexample. As a result, as illustrated in FIG. 22B, a current Ic flows tothe transistor 234, thereby increasing the DC receiving current Idc. Inthis way, the current increasing control is performed to increase the DCreceiving current Idc to the threshold current Ith or more (Idc≧Ith).

Here, FIG. 23 and FIG. 24 each illustrate a measurement result exampleaccording to Modification 3, both in a case (Example) in which thecurrent increasing control section 23 is provided, and in a case (acomparative example) in which the current increasing control section 23is not provided. Specifically, FIG. 23 illustrates the measurementresult example indicating a relationship between the DC receivingcurrent Idc and the DC receiving voltage Vdc, and FIG. 24 illustratesthe measurement result example indicating temporal variations of the ACreceiving voltage Vac. It is to be noted that in each of thesemeasurement result examples, a result similar to a simulation wasobtained.

It is apparent from FIG. 23 that an abrupt rise in the DC receivingvoltage Vdc when the DC receiving current Idc is small is avoided byproviding the current increasing control section 23A. Further, it isapparent from FIG. 24 that ringing in the AC receiving voltage Vac dueto a harmonic is suppressed by providing the current increasing controlsection 23A, so that a rise in voltage is suppressed.

Further, FIG. 25 illustrates a measurement result example indicating arelationship between the reference voltage Vref and each parameter (theDC receiving voltage Vdc, the threshold current Ith, and the loadresistance value). FIG. 25 illustrates the example in the case of thecircuit configuration (the configuration in which the DC receivingvoltage Vdc that is a variable voltage is used as the input voltageVin1) illustrated in FIG. 21B. It is apparent from FIG. 25 that, in thecase of the circuit configuration, even when the DC receiving voltageVdc changes, the reference voltage Vref (the threshold current Ith) alsochanges accordingly as described above. Therefore, as a result, thevalue of the load resistance is kept constant. Specifically, in thiscase, as the DC receiving voltage Vdc rises, the reference voltage Vref(the threshold current Ith) increases. Therefore, the current (the DCreceiving current Idc) flows more, so that the load resistance valueremains constant.

As described above, in the present modification, when the DC receivingcurrent Idc at the time of the light load is less than the thresholdcurrent Ith, the current increasing control section 23A performs thecurrent increasing control, to increase the DC receiving current Idc tothe threshold current Ith or more. This makes it possible to control thereceiving voltage (such as the DC receiving voltage Vdc) in theelectronic unit 2A readily in an appropriate manner, even at the time ofthe light load. Specifically, it is possible to avoid a possibility ofthe receiving voltage being brought into an uncontrollable state, or apossibility of the receiving voltage becoming an overvoltage, due to thelight load, as described with reference to FIG. 8, for example.Therefore, like the above-described embodiment, it is possible toperform appropriate control in the feeding using a magnetic field.

Further, in the present modification, in particular, it is possible toperform autonomous (active) current increasing control, and it is alsopossible to perform continuous, not stepping (discontinuous), currentincreasing control, unlike the case of the current increasing controlutilizing the dummy load circuit 23 described in the above-describedembodiment.

Furthermore, when the reference voltage Vref, which is a variablevoltage that varies in connection with a change in the DC receivingvoltage Vdc, is generated by dividing the DC receiving voltage Vdc, asillustrated in FIG. 21B, for example, it is possible to obtain thefollowing effect. For example, in a case such as when a voltagefluctuation of the DC receiving current Idc is large, maintaining theload resistance value constant using such a circuit configuration mayproduce an effect larger than that of the case of maintaining the DCreceiving current Idc constant.

[Modification 4]

(Configuration)

FIG. 26 illustrates a circuit configuration example of a currentincreasing control section (a current increasing control section 23B)according to Modification 4. The current increasing control section 23Bof the present modification corresponds to a current increasing controlsection in which a reference-voltage output section 231B is provided inplace of the reference-voltage output section 231 in the currentincreasing control section 23 (the configuration of FIG. 21B) describedin Modification 3, and operation of the reference-voltage output section231B is controlled by the control section 27A. The present modificationis similar to Modification 3 in terms of other configurations.

The reference-voltage output section 231B is capable of changing avoltage division ratio in dividing the DC receiving voltage Vdc in thereference-voltage output section 231 illustrated in FIG. 21B.Specifically, in the reference-voltage output section 231B, tworesistors 231R1 a and 231R1 b connected in parallel to each other areprovided in place of the resistor 231R1 illustrated in FIG. 21B, and aswitching element SW31 that is configured of a MOS transistor or thelike is connected in series to the resistor 231R1 b. Similarly, tworesistors 231R2 a and 231R2 b connected in parallel to each other areprovided in place of the resistor 231R2 illustrated in FIG. 21B, and aswitching element SW32 that is configured of a MOS transistor or thelike is connected in series to the resistor 231R2 b. The switchingelements SW31 and SW32 are individually controlled to be in an ON stateand an OFF state, according to control signals CTL31 and CTL32,respectively, supplied from the control section 27A (see an arrow of abroken line in FIG. 26).

In the reference-voltage output section 231B, the ON/OFF state of eachof the switching elements SW31 and SW32 is thus individually controlledso that the voltage division ratio (the resistance ratio) in dividingthe DC receiving voltage Vdc changes as described above. Therefore, inthe current increasing control section 23B of the present modification,it is possible to change the value of the reference voltage Vrefaccording to the control by the control section 27A, and it is alsopossible to obtain, for example, the following effect, in addition tothe effects in Modification 3.

In the current increasing control section 23A described in Modification3, dynamic control by the control section 27A is basically unnecessaryso that standalone operation is possible, which is a great advantage.Meanwhile, when non-contact feeding is performed, there are a pluralityof phases such as an initial operation phase, a communication phase, anda feeding phase, in many cases. In addition, it is conceivable to changea topology according to electric power and therefore, it is alsoconceivable to change a current value and a load resistance value to becontrolled, for each one of the plurality of phases. Therefore, thecurrent increasing control section 23B of the present modification isused to make it possible to change a control value (such as the currentvalue and the load resistance value) in a specific phase, by activelyperforming load control with an initial parameter, without performingthe dynamic control by the control section 27A that is unnecessary.

Moreover, like the case in which the current value is controlled, it ispossible to avoid a possibility of the DC receiving voltage Vdc becomingan overvoltage, etc., by controlling the load resistance value to beless than a certain value.

It is to be noted that, the present modification is configured such thatthe voltage division ratio is changed utilizing the ON/OFF state of eachof the switching elements SW31 and SW32, but is not limited thereto. Forexample, the voltage division ratio may be changed using a variableresistor as each of the resistors 231R1 and 231R2 illustrated in FIG.21B.

[Other Modifications]

The technology of the present disclosure has been described withreference to the embodiment and the modifications. However, the presenttechnology is not limited to these embodiments and the like, and may bevariously modified.

For example, the description has been provided using various coils (thepower transmission coil, and the power receiving coil) in theabove-described embodiment and the like, but various kinds ofconfigurations may be used as the configurations (the shapes) of thesecoils. In other words, each coil may have, for example, a shape such asa spiral shape, a loop shape, a bar shape using a magnetic substance, anα-winding shape in which a spiral coil is folded to be in two layers, aspiral shape having more multiple layers, a helical shape in which awinding is wound in a thickness direction, etc. In addition, each coilmay be not only a winding coil configured using a wire rod havingconductivity, but also a pattern coil having conductivity and configuredusing, for example, a printed circuit board, a flexible printed circuitboard, etc.

Further, in the above-described embodiment and the like, an electronicunit has been described as an example of the unit to be fed, but theunit to be fed is not limited thereto and may be any type of unit to befed other than electronic units (e.g. a vehicle such as an electriccar).

Furthermore, in the above-described embodiment and the like, eachcomponent of the feed unit and the electronic unit has been specificallydescribed. However, it is not necessary to provide all the components,or other component may be further provided. For example, a communicationfunction, a function of performing some kind of control, a displayfunction, a function of authenticating a secondary-side unit, a functionof detecting a mixture such as dissimilar metal, and/or the like may beprovided in the feed unit and/or the electronic unit. In addition, theconfigurations of the current increasing section (the dummy loadcircuit) and the current increasing control section, as well as thetechniques of increasing the current, may also be other configurationsand techniques, without being limited to those of the above-describedembodiment and the like. Specifically, for example, the number of thedummy loads in the dummy load circuit may be one, or three or more,without being limited to the number (two) described in theabove-described embodiment and the like. Further, for example, insteadof the PI control, PID (Proportional Integral Derivative) control may beperformed in the current increasing control section. Furthermore, in theabove-described embodiment and the like, “the time of the light load” atwhich the current increasing control is to be performed has beendescribed by taking, as an example, both of the period of thepreliminary feeding (the first period) and the period of the chargingoperation (the second period) for the secondary battery based on themain feeding, but is not limited thereto. For example, only one of thefirst period and the second period may be used as “the time of the lightload”, at which the current increasing control is to be performed.

In addition, the above-described embodiment and the like have beendescribed by taking, as an example, the case in which the receivingcurrent (the DC receiving current Idc) after the rectification by therectification circuit 21 is detected by the current detection section22, and but is not limited thereto. For example, the receiving current(the AC receiving current Iac) before the rectification by therectification circuit 21 may be detected and used for the currentincreasing control. Alternatively, a current (a load current) flowing tothe battery 25 may be detected as the receiving current. However, it maybe said that it is desirable to detect the DC receiving current Idc,because it is easier to detect the DC receiving current Idc than the ACreceiving current Iac. It is to be noted that, in the above-describedembodiment and the like, the dummy load circuit 23 as well as thecurrent increasing control sections 23A and 23B are each disposed on thesubsequent stage side of the rectification circuit 21, but the positionsthereof are not limited thereto. For example, these sections each may bedisposed on a preceding stage side of the rectification circuit 21.

In addition, the above-described embodiment and the like have beendescribed by taking mainly the case in which only one electronic unit isprovided in the feed system as an example. However, the technology isnot limited thereto, and a plurality of (two or more) electronic unitsmay be provided in the feed system.

Moreover, the above-described embodiment and the like have beendescribed by taking the charging tray for the small electronic unit (theCE device) such as a mobile phone, as an example of the feed unit.However, the feed unit is not limited to such a home charging tray, andmay be applicable to battery chargers of various kinds of electronicunits. In addition, it is not necessarily for the feed unit to be atray, and may be, for example, a stand for an electronic unit such as aso-called cradle.

It is to be noted that the effects described in the presentspecification are only examples, and the present technology may haveother effects without being limited thereto.

It is to be noted that the present technology may be configured asfollows.

-   -   (1) An electronic unit including:    -   a power receiving section configured to receive electric power        fed from a feed unit by using a magnetic field; and    -   a control section configured to perform, when a receiving        current supplied from the power receiving section is less than a        predetermined threshold current at a time of a light load,        current increasing control to increase the receiving current to        the threshold current or more.    -   (2) The electronic unit according to (1), further including    -   a current increasing section including one or a plurality of        dummy loads,    -   wherein the control section performs the current increasing        control by utilizing one or more of the dummy loads.    -   (3) The electronic unit according to (2), wherein    -   when the receiving current is less than the threshold current,    -   the control section performs the current increasing control, by        connecting one or more of the dummy loads to a point in a supply        path of the receiving current, and controlling a current to flow        to the connected dummy loads.    -   (4) The electronic unit according to (3), wherein the control        section disconnects the dummy loads from the point in the supply        path when a main load is set in a connection state.    -   (5) The electronic unit according to (3), wherein the control        section disconnects the dummy loads from the point in the supply        path when the receiving current is equal to or more than the        threshold current, after a main load is set in a connection        state.    -   (6) The electronic unit according to any one of (3) to (5),        wherein    -   the current increasing section includes a plurality of types of        the dummy loads different in magnitude of load from one another,        and    -   when the receiving current is less than the threshold current,    -   the control section connects, to the point in the supply path,        the dummy load of a type that is selected from the plurality of        types of the dummy loads according to a magnitude of the        receiving current.    -   (7) The electronic unit according to (6), wherein the control        section connects the dummy load to the point in the supply path,        the connected dummy load being relatively large, as the        receiving current becomes small.    -   (8) The electronic unit according to any one of (3) to (7),        wherein    -   when the receiving current is still less than the threshold        current, after one or more of the dummy loads are connected to        the point in the supply path of the receiving current,    -   the control section additionally connects the dummy load to the        point in the supply path, or switches the dummy load to the        dummy load having a larger load.    -   (9) The electronic unit according to (1), wherein the control        section includes,    -   a comparator configured to compare a magnitude of a receiving        voltage corresponding to the receiving current, with a magnitude        of a reference voltage corresponding to the threshold current,    -   an integrator configured to receive an output signal from the        comparator, and    -   a transistor configured to operate according to control by the        integrator.    -   (10) The electronic unit according to (9), wherein    -   when the receiving voltage is determined to be less than the        reference voltage, based on the output signal,    -   the integrator performs the current increasing control, by        connecting the transistor to the point in the supply path of the        receiving current, and controlling a current to flow to the        transistor.    -   (11) The electronic unit according to (9) or (10), wherein the        reference voltage is a constant voltage.    -   (12) The electronic unit according to (9) or (10), wherein the        reference voltage is a variable voltage that varies in        connection with a change in the receiving voltage.    -   (13) The electronic unit according to any one of (9) to (12),        wherein    -   the reference voltage is generated by dividing a predetermined        fixed voltage or the receiving voltage, and    -   a value of the reference voltage is modifiable by changing a        voltage division ratio in the dividing.    -   (14) The electronic unit according to any one of (1) to (13),        wherein the time of the light load is either one of    -   a first period in which preliminary feeding of power lower than        power of main feeding is performed by the feed unit, and    -   a second period in which a secondary battery serving as a main        load is set in a connection state, and operation of charging the        secondary battery is performed based on the main feeding, the        second period following the first period.    -   (15) The electronic unit according to (14), wherein    -   while the charging operation is performed in the second period,    -   whether the receiving current is less than the threshold current        is periodically determined.    -   (16) The electronic unit according to (14) or (15), wherein    -   after increasing the receiving current to the threshold current        or more in the first period,    -   the control section notifies the feed unit of a request for        start of the main feeding.    -   (17) The electronic unit according to any one of (1) to (16),        wherein a value of the threshold current is modifiable.    -   (18) The electronic unit according to any one of (1) to (17),        further including a current detection section configured to        detect the receiving current,    -   wherein the control section performs the current increasing        control, by using the receiving current detected by the current        detection section.    -   (19) The electronic unit according to (18), further including    -   a rectification circuit configured to rectify the receiving        current,    -   wherein the current detection section detects a receiving        current after rectification by the rectification circuit.    -   (20) A feed system provided with one or a plurality of        electronic units and a feed unit configured to feed the        electronic units by using a magnetic field, each of the        electronic units including:    -   a power receiving section configured to receive electric power        fed from the feed unit; and    -   a control section configured to perform, when a receiving        current supplied from the power receiving section is less than a        predetermined threshold current at a time of a light load,        current increasing control to increase the receiving current to        the threshold current or more.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An electronic unit comprising: power receivingcircuitry configured to receive electric power fed from a feed unit byusing a magnetic field; control circuitry configured to perform, when areceiving current supplied from the power receiving circuitry is lessthan a predetermined threshold current at a time of a light load,current increasing control to increase the receiving current to thethreshold current or more; and current increasing circuitry includingone or a plurality of dummy loads, wherein the control circuitryperforms the current increasing control by utilizing one or more of thedummy loads.
 2. The electronic unit according to claim 1, wherein whenthe receiving current is less than the threshold current, the controlcircuitry performs the current increasing control, by connecting one ormore of the dummy loads to a point in a supply path of the receivingcurrent, and controlling a current to flow to the connected dummy loads.3. The electronic unit according to claim 2, wherein the controlcircuitry disconnects the dummy loads from the point in the supply pathwhen a main load is set in a connection state.
 4. The electronic unitaccording to claim 2, wherein the control circuitry disconnects thedummy loads from the point in the supply path when the receiving currentis equal to or more than the threshold current, after a main load is setin a connection state.
 5. The electronic unit according to claim 2,wherein the current increasing circuitry includes a plurality of typesof the dummy loads different in magnitude of load from one another, andwhen the receiving current is less than the threshold current, thecontrol circuitry connects, to the point in the supply path, the dummyload of a type that is selected from the plurality of types of the dummyloads according to a magnitude of the receiving current.
 6. Theelectronic unit according to claim 5, wherein the control circuitryconnects the dummy load to the point in the supply path, the connecteddummy load being relatively large, as the receiving current becomessmall.
 7. The electronic unit according to claim 2, wherein when thereceiving current is still less than the threshold current, after one ormore of the dummy loads are connected to the point in the supply path ofthe receiving current, the control circuitry additionally connects thedummy load to the point in the supply path, or switches the dummy loadto the dummy load having a larger load.
 8. The electronic unit accordingto claim 1, wherein the control circuitry includes, a comparatorconfigured to compare a magnitude of a receiving voltage correspondingto the receiving current, with a magnitude of a reference voltagecorresponding to the threshold current, an integrator configured toreceive an output signal from the comparator, and a transistorconfigured to operate according to control by the integrator.
 9. Theelectronic unit according to claim 8, wherein when the receiving voltageis determined to be less than the reference voltage, based on the outputsignal, the integrator performs the current increasing control, byconnecting the transistor to the point in the supply path of thereceiving current, and controlling a current to flow to the transistor.10. The electronic unit according to claim 8, wherein the referencevoltage is a constant voltage.
 11. The electronic unit according toclaim 8, wherein the reference voltage is a variable voltage that variesin connection with a change in the receiving voltage.
 12. The electronicunit according to claim 8, wherein the reference voltage is generated bydividing a predetermined fixed voltage or the receiving voltage, and avalue of the reference voltage is modifiable by changing a voltagedivision ratio in the dividing.
 13. The electronic unit according toclaim 1, wherein the time of the light load is either one of a firstperiod in which preliminary feeding of power lower than power of mainfeeding is performed by the feed unit, and a second period in which asecondary battery serving as a main load is set in a connection state,and operation of charging the secondary battery is performed based onthe main feeding, the second period following the first period.
 14. Theelectronic unit according to claim 13, wherein while the chargingoperation is performed in the second period, whether the receivingcurrent is less than the threshold current is periodically determined.15. The electronic unit according to claim 13, wherein after increasingthe receiving current to the threshold current or more in the firstperiod, the control circuitry notifies the feed unit of a request forstart of the main feeding.
 16. The electronic unit according to claim 1,wherein a value of the threshold current is modifiable.
 17. Anelectronic unit comprising: power receiving circuitry configured toreceive electric power fed from a feed unit by using a magnetic field;control circuitry configured to perform, when a receiving currentsupplied from the power receiving circuitry is less than a predeterminedthreshold current at a time of a light load, current increasing controlto increase the receiving current to the threshold current or more; anda current detection circuitry configured to detect the receivingcurrent, wherein the control circuitry performs the current increasingcontrol, by using the receiving current detected by the currentdetection circuitry.
 18. The electronic unit according to claim 17,further comprising a rectification circuit configured to rectify thereceiving current, wherein the current detection circuitry detects areceiving current after rectification by the rectification circuit. 19.A feed system provided with one or a plurality of electronic units and afeed unit configured to feed the electronic units by using a magneticfield, each of the electronic units comprising: power receivingcircuitry configured to receive electric power fed from the feed unit;control circuitry configured to perform, when a receiving currentsupplied from the power receiving circuitry is less than a predeterminedthreshold current at a time of a light load, current increasing controlto increase the receiving current to the threshold current or more; andcurrent increasing circuitry including one or a plurality of dummyloads, wherein the control circuitry performs the current increasingcontrol by utilizing one or more of the dummy loads.
 20. An electronicunit comprising: a power receiving section configured to receiveelectric power fed from a feed unit by using a magnetic field; a controlsection configured to perform, when a receiving current supplied fromthe power receiving section is less than a predetermined thresholdcurrent at a time of a light load, current increasing control toincrease the receiving current to the threshold current or more; and acurrent increasing section including one or a plurality of dummy loads,wherein the control section performs the current increasing control byutilizing one or more of the dummy loads.
 21. An apparatus comprising:power receiving circuitry including a coil, the power receiving circuitybeing configured to receive electric power fed from a feed unit by usinga magnetic field; a memory; and a controller in communication with thememory and configured to perform, when a receiving current supplied fromthe power receiving circuitry is less than a predetermined thresholdcurrent at a time of a light load, current increasing control toincrease the receiving current to the threshold current or more, whereinthe controller performs the current increasing control by utilizing oneor more of a plurality of dummy loads.